Gary Cahill ensures back issue is on the agenda again for Chelsea

Jose Mourinho is paid a lot to make difficult decisions and life will be no easier for him this week despite a fine win in the Champions League.

With Chelsea’s progress to the last 16 back on track following this convincing victory at Schalke, Mourinho has a number of issues to address before Sunday’s match against title rivals ­Manchester City.

For example, who plays up front? Samuel Eto’o finally got off the mark with an impressive performance against Cardiff on Saturday, yet last night Fernando Torres netted twice on his 100th start for the club to ­virtually beat the German side on his own.

Chelsea have often lost the midfield battle against City in recent encounters and the partnership of Ramires and Frank Lampard is still not offering the back four enough protection. The prospect of John Obi Mikel being recalled to the starting line-up is surely a possibility.

These are all still pleasant problems to have, however, the one poser that could haunt Mourinho throughout the campaign, let alone the next few days, is who should be his first-choice central defensive partnership.

In truth, he got his answer here inside the volatile atmosphere of the Veltins-Arena, where captain John Terry and Gary Cahill repelled Schalke at every turn.

Remarkably this was Cahill’s first appearance for Chelsea in four weeks, although two matches for England ensured he was match fit.

Watching from the sidelines was David Luiz, who was seemingly dropped by Mourinho for the sloppy error he made on Saturday when he allowed Cardiff’s Jordon Mutch to run onto Ramires’s back pass to score past goalkeeper Petr Cech.

When fully focused, Luiz is a fine defender and one of the best footballers at the club. His infectious personality also has a hugely positive effect on the team but the Brazil international becomes a liability on the occasions he is off kilter.

Arguably, his best performances for Chelsea have come when playing in central midfield, where any errors are less likely to be punished as severely.

Mourinho has so far appeared to be opposed to the idea, which was ­introduced to good effect by interim manager Rafael Benitez last term.

It is unlikely he will have a change of heart for the visit of City but Cahill’s showing alongside Terry must make him think twice about recalling Luiz to face Sergio Aguero and Co.

The English duo certainly seem to have a more natural partnership and trust in what each other is doing. Sometimes you get the impression they are not so confident in their decision making when Luiz is next to them.

Mourinho, who is estimated to be paid £8.5million a year, is aware what a fine line his selection policy can be.

When asked about the idea behind picking Cahill, as well as Cesar Azpilicueta to play left-back against Schalke, he said: “Decisions are interesting when you win and when the players give you reason [to do it] but when things go wrong it’s difficult. I’m here to try and make the best ­decisions. I try to anticipate what the game is.

“The team were stable and we could kill the game in counter-attack. But to do that, you have to defend well. If you don’t defend well, you can’t counter- attack. Of course people in attack resolve situations for us but the defensive block gives us great stability.”

Few will be surprised if Luiz returns to the back four at the weekend, yet the debate is sure to run and run.

Crucially, Chelsea will go into the match full of confidence. They are now seven matches unbeaten in all competitions and successive away wins in the Champions League have put them top of Group E.

Eden Hazard continued his return to form with another fine goal to seal the victory against Schalke after Torres’s brace had already silenced the home fans.

The smiles and positive body ­language after the final whistle were a far cry from the misery that was on view just over a month ago following their defeat to Basle in the opening group game.

Mourinho added: “The good thing for me was the way we coped with the pressure. We lost at home in the first game and we were in trouble. Many people were panicking and thinking we’re going to the Europa League again.

“The way the team coped with that pressure to come to two consecutive matches away [they beat Steaua Bucharest 4-0 earlier this month] and get six points to put us top of the group, I think it’s important the way the team psychologically reacted to that.”